1. Field of the Invention
The present invention relates to a solid-state imaging device, a solid-state imaging device manufacturing method, an electronic device, and a lens array.
2. Description of the Related Art
Cameras such as digital video cameras and digital still cameras include solid-state imaging devices, e.g., include CMOS (Complementary Metal Oxide Semiconductor) image sensors or CCD (Charge Coupled Device) image sensors as a solid-state imaging device.
With solid-state imaging devices, an imaging region where multiple pixels are formed is provided to the surface of the semiconductor substrate. With this imaging region, multiple photoelectric conversion units which receive light according to a subject image, and generate signal charge by subjecting the received light thereof to photoelectric conversion, are formed so as to correspond to the multiple pixels thereof. For example, photodiodes are formed as the photoelectric conversion units.
Of solid-state imaging devices, with CCD-type image sensors, a vertical transfer register unit is provided between multiple pixel columns arrayed in the vertical direction. With vertical transfer register units, multiple transfer electrodes are provided so as to face a vertical transfer channel region via a gate insulating film, which transfer signal charge read out from a photoelectric conversion unit by a charge readout unit in the vertical direction. Subsequently, the signal charge transferred for each one horizontal line (pixels in one row) by the vertical transfer register unit thereof is transferred in the horizontal direction by a horizontal transfer register unit, and is output by an output unit.
Also, of solid-state imaging devices, with CMOS-type image sensors, pixels are configured so as to include multiple transistors in addition to photoelectric conversion units. The multiple transistors are configured as a pixel transistor which reads out the signal charge generated by a photoelectric conversion unit to output this to a signal line as an electric signal. Also, with CMOS-type image sensors, in order to reduce the pixel size, it has been proposed that the pixels be configured so that the multiple photoelectric conversion units share the above pixel transistor. For example, a technique has been proposed wherein two or four photoelectric conversion units share a single pixel transistor group (e.g., see Japanese Unexamined Patent Application Publication No. 2004-172950).
With solid-state imaging devices, in general, a “front illumination” type has been familiar wherein photoelectric conversion units receive light to be input from the surface side where circuit elements and wirings and so forth are provided on the semiconductor substrate. In the case of the front illumination type, there is a case where it is difficult to improve sensitivity since a circuit element or wiring or the like shield or reflect light to be input thereto. Therefore, a “backside illumination” type has been proposed wherein photoelectric conversion units receive light to be input from the rear surface side that is the opposite side of the surface where circuit elements, wirings, and so forth are provided on the semiconductor substrate (e.g., see Japanese Unexamined Patent Application Publication No. 2003-31785).
With a solid-state imaging device such as described above, as the number of pixels increases, the cell size of each pixel becomes small. As a result thereof, light receiving amount per one pixel may decrease.
Therefore, in order to enhance the light collection efficiency and increase the amount of light received, an on-chip lens is provided. Specifically, a micro lens for focusing light onto the light-receiving surface of a photoelectric conversion unit is provides so as to correspond to each pixel (e.g., see Japanese Unexamined Patent Application Publication Nos. 2000-039503 and 2000-206310).
With micro lens forming process, for example, a micro lens material configured of a photosensitive resin is subjected to pattern processing on a flattened film (or undercoating of a micro lens) disposed on a color filter by photolithography technology. Subsequently, the processed micro lens material is subjected to bleaching exposure, and is subsequently subjected to a reflow process, and accordingly a micro lens is formed (e.g., see Japanese Unexamined Patent Application Publication Nos. 2003-222705, 2007-294779, and 2007-025383).
In addition, after a mask layer is formed on a lens material layer, a micro lens is formed by subjecting the lens material layer to etching processing using the mask layer thereof. Specifically, first, after a photosensitive resin film is formed on the lens material layer, the photosensitive resin is subjected to pattern processing by photolithography to form a resist pattern so as to correspond to a region where a micro lens is formed. Subsequently, a reflow process for heating and melting the resist pattern is carried out to transform the resist pattern thereof into the shape of the lens, thereby forming a mask layer. Subsequently, both of the resist pattern transformed into the mask layer thereof, and the lens material layer are subjected to etchback, and accordingly, the lens material layer located under the mask layer is processed into a macro lens (e.g., see Japanese Patent No. 4186238, and Japanese Unexamined Patent Application Publication No. 2007-53318).